This invention relates generally to speed sensor systems for sensing rotational speed, and, more particularly, to a sensor system suitable for semi- or full floating type axles with drawn cup wheel bearings.
Typically, semi- or full floating type axles are used for the wheels of pickup trucks and rear wheel drive passenger cars. A drawn cup wheel bearing may be pressed into the axle tube with rollers of the bearing riding directly on the axle shaft, thereby providing a low cost bearing that requires very little axial space and is capable of carrying high loads. However, when a drawn cup wheel bearing is used on such axles, the drawn cup wheel bearing provides no axial support of the axle shaft because the axle shaft is typically retained with a mechanical interlock at the inboard end of the axle shaft. As a result of the reduced axial support, the axle shaft pivots at the bearing, creating a slope of the axle shaft through the bearing when the axle shaft is under axial or radial loads.
Common variable reluctance type speed sensor systems use. a tone wheel or gear as a target and a magnet, coil of wire and metallic pole piece as a sensor. These are generally mounted at the end of the axle shaft with the tone wheel pressed on a step formed in the back of a vehicle mounting flange. If such sensor systems were used with a drawn cup wheel bearing on a semi- or full floating type axle, the slope of the axle shaft through the drawn cup wheel bearing would cause the critical air gap between the target and sensor to fluctuate and reduce signal accuracy. Because of this incompatibility with such speed sensor systems, several axle applications that have traditionally used drawn cup wheel bearings have switched to more expensive and larger radial ball bearings or tapered roller bearings with machined races in order to reduce the axle shaft slope.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed
to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is accomplished by providing a sensor system for sensing axle shaft speed comprising an axle tube, a drawn cup wheel bearing mounted within the axle tube, and an axle shaft mounted in the drawn cup wheel bearing with a vehicle mounting flange of the axle shaft positioned axially outwardly of the axle tube. An annular target is supported from the vehicle mounting flange of the axle shaft such that the target is positioned axially inwardly of the vehicle mounting flange and is positioned over the axle tube. A sensor is supported from the:axle tube over the annular target for sensing rotation of the annular target.
The foregoing and other aspects will become apparent from, the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.